Optical fibers connectors are used to terminate optical fibers. Optical fiber connectors may also be used to mechanically retain two optical fibers such that light carried by one optical fiber can couple into a corresponding optical fiber to form a light-transmitting path between them. A multitude of optical fiber connector types have been developed over the years for specific purposes including PC, SMA, LC and ST-type connectors. The well-known FC-type optical fiber connector for example offers high alignment accuracy with up to 500 mating cycles and finds application in the telecommunications field where a small misalignment between the optical fiber cores results in significant optical insertion losses.
Owing to variations in manufacturing tolerance and age-related degradation of materials, the transmittance of the optical path of an optical fiber connector may be subject to some variations. Some applications, particularly optical test and measurement applications, are highly sensitive to changes in the absolute, and/or relative transmittance of different wavelengths of light carried by optical fibers because such changes lead to errors in measured signals. The ability to calibrate the optical path of an optical fiber therefore finds importance in optical test and measurement equipment. In one exemplary application in the optical test and measurement field, a so-called photonic needle disclosed in document “Estimation of lipid and water concentrations in scattering media with diffuse optical spectroscopy from 900 to 1600 nm”, J. Biomed. Opt. 15, 037015 (2010) by R. Nachabé, B. H. W. Hendriks, A. E. Desjardins, M. van der Voort, M. B. van der Mark, and H. J. C. M. Sterenborg, uses optical fibers to deliver light and perform spectral sensing measurements at the tip of a needle in order to analyze tissue that is in contact with the needle tip. In this example application an optical source and an optical measurement apparatus are housed within a console. Optical radiation generated by the optical source is transmitted to the needle tip by a delivery optical fiber where it interacts with tissue that is in contact with the needle tip. Following interaction of the light emitted by the delivery optical fiber with the tissue, return light is collected by a collection optical fiber and is conveyed to the optical measurement apparatus within the console. The optical interaction may include for example diffuse or specular reflections from the tissue, or fluorescence emission from chromophores in the tissue or the presence of a fluorescent marker in the tissue. The return light may therefore include for example diffusely or specularly reflected light, Raman scattered light, or fluorescence emission light. The tissue may subsequently be analyzed by comparing the spectral content of the light collected by the collection optical fiber with that of the light emitted by the delivery optical fiber. Owing to the sensitive nature of this spectral analysis, variations in the transmission spectrum of the optical fibers used in delivering and collecting the optical signals may confound analysis. In particular it is the relative variations in this transmission spectrum that lead to errors. Thus, it may be beneficial to measure the transmission spectrum of the delivery optical fiber and the collection optical fiber before use in order to carry out a calibration. Such a calibration may also be beneficial in calibrating against variations in the optical performance of other optical components in the optical measurement path, including spectrometers and light sources because the sensitivity, emissivity and attenuation as a function of wavelength and environmental parameters of these optical components may also vary. Thus, it may be beneficial to calibrate the entire optical path between the optical source and the optical detector in order to improve the accuracy of the analysis.
One device for calibrating a fiber optic probe such as a catheter is disclosed in U.S. Pat. No. 4,050,450. This patent discloses to use a attach a generally tubular reflecting member to the distal end of the catheter such that light delivered by a delivery optical fiber located within the catheter is reflected into a collection optical fiber within the catheter. The optical path is subsequently calibrated based on the optical reflectance of the tubular member.
Another device for calibrating the optical path of an optical fiber is disclosed in U.S. Pat. No. 7,005,623B2. This patent discloses a calibration sheath having one or more detectors on its interior surface. In use, the detectors measure a portion of the emitted radiation which is used to adjust the transmitted power in order to conform to desired treatment parameters.
However, a drawback of the additional components required by these solutions is that they complicate workflow.